We'd encourage this to be written as a plugin, which can add new compute resources. We've already got foreman_digitalocean, foreman_one and foreman_xen - I'd look at the DO plugin as a good template.

The plugin would just need to depend on fog-azure in its gemspec file.

http://projects.theforeman.org/projects/foreman/wiki/How_to_Create_a_Plugin has general information for setting up a plugin, including a template plugin.